Date: Tue, 29 Jan 2019 20:35:09 +0000 (UTC) From: Alexander Motin <mav@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r343562 - head/sys/dev/nvd Message-ID: <201901292035.x0TKZ9Yj006529@repo.freebsd.org>
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Author: mav Date: Tue Jan 29 20:35:09 2019 New Revision: 343562 URL: https://svnweb.freebsd.org/changeset/base/343562 Log: Reimplement BIO_ORDERED handling in nvd(4). This fixes BIO_ORDERED semantics while also improving performance by: - sleeping also before BIO_ORDERED bio, as defined, not only after; - not queueing BIO_ORDERED bio to taskqueue if no other bios running; - waking up sleeping taskqueue explicitly rather then rely on polling. On Samsung SSD 970 PRO this shows sync write latency, measured with `diskinfo -wS`, reduction from ~2ms to ~1.1ms by not sleeping without reason till next HZ tick. On the same device ZFS pool with 8 ZVOLs synchronously writing 4KB blocks shows ~950 IOPS instead of ~750 IOPS before. I suspect ZFS does not need BIO_ORDERED on BIO_FLUSH at all, but that will be next question. MFC after: 2 weeks Sponsored by: iXsystems, Inc. Modified: head/sys/dev/nvd/nvd.c Modified: head/sys/dev/nvd/nvd.c ============================================================================== --- head/sys/dev/nvd/nvd.c Tue Jan 29 20:10:27 2019 (r343561) +++ head/sys/dev/nvd/nvd.c Tue Jan 29 20:35:09 2019 (r343562) @@ -82,6 +82,7 @@ struct nvd_disk { struct nvme_namespace *ns; uint32_t cur_depth; +#define NVD_ODEPTH (1 << 31) uint32_t ordered_in_flight; u_int unit; @@ -181,39 +182,50 @@ nvd_unload() mtx_destroy(&nvd_lock); } -static int +static void nvd_bio_submit(struct nvd_disk *ndisk, struct bio *bp) { int err; bp->bio_driver1 = NULL; - atomic_add_int(&ndisk->cur_depth, 1); + if (__predict_false(bp->bio_flags & BIO_ORDERED)) + atomic_add_int(&ndisk->cur_depth, NVD_ODEPTH); + else + atomic_add_int(&ndisk->cur_depth, 1); err = nvme_ns_bio_process(ndisk->ns, bp, nvd_done); if (err) { - atomic_add_int(&ndisk->cur_depth, -1); - if (__predict_false(bp->bio_flags & BIO_ORDERED)) + if (__predict_false(bp->bio_flags & BIO_ORDERED)) { + atomic_add_int(&ndisk->cur_depth, -NVD_ODEPTH); atomic_add_int(&ndisk->ordered_in_flight, -1); + wakeup(&ndisk->cur_depth); + } else { + if (atomic_fetchadd_int(&ndisk->cur_depth, -1) == 1 && + __predict_false(ndisk->ordered_in_flight != 0)) + wakeup(&ndisk->cur_depth); + } bp->bio_error = err; bp->bio_flags |= BIO_ERROR; bp->bio_resid = bp->bio_bcount; biodone(bp); - return (-1); } - - return (0); } static void nvd_strategy(struct bio *bp) { - struct nvd_disk *ndisk; + struct nvd_disk *ndisk = (struct nvd_disk *)bp->bio_disk->d_drv1; - ndisk = (struct nvd_disk *)bp->bio_disk->d_drv1; - - if (__predict_false(bp->bio_flags & BIO_ORDERED)) - atomic_add_int(&ndisk->ordered_in_flight, 1); - - if (__predict_true(ndisk->ordered_in_flight == 0)) { + /* + * bio with BIO_ORDERED flag must be executed after all previous + * bios in the queue, and before any successive bios. + */ + if (__predict_false(bp->bio_flags & BIO_ORDERED)) { + if (atomic_fetchadd_int(&ndisk->ordered_in_flight, 1) == 0 && + ndisk->cur_depth == 0 && bioq_first(&ndisk->bioq) == NULL) { + nvd_bio_submit(ndisk, bp); + return; + } + } else if (__predict_true(ndisk->ordered_in_flight == 0)) { nvd_bio_submit(ndisk, bp); return; } @@ -281,28 +293,27 @@ nvd_ioctl(struct disk *ndisk, u_long cmd, void *data, static int nvd_dump(void *arg, void *virt, vm_offset_t phys, off_t offset, size_t len) { - struct nvd_disk *ndisk; - struct disk *dp; + struct disk *dp = arg; + struct nvd_disk *ndisk = dp->d_drv1; - dp = arg; - ndisk = dp->d_drv1; - return (nvme_ns_dump(ndisk->ns, virt, offset, len)); } static void nvd_done(void *arg, const struct nvme_completion *cpl) { - struct bio *bp; - struct nvd_disk *ndisk; + struct bio *bp = (struct bio *)arg; + struct nvd_disk *ndisk = bp->bio_disk->d_drv1; - bp = (struct bio *)arg; - - ndisk = bp->bio_disk->d_drv1; - - atomic_add_int(&ndisk->cur_depth, -1); - if (__predict_false(bp->bio_flags & BIO_ORDERED)) + if (__predict_false(bp->bio_flags & BIO_ORDERED)) { + atomic_add_int(&ndisk->cur_depth, -NVD_ODEPTH); atomic_add_int(&ndisk->ordered_in_flight, -1); + wakeup(&ndisk->cur_depth); + } else { + if (atomic_fetchadd_int(&ndisk->cur_depth, -1) == 1 && + __predict_false(ndisk->ordered_in_flight != 0)) + wakeup(&ndisk->cur_depth); + } biodone(bp); } @@ -320,22 +331,23 @@ nvd_bioq_process(void *arg, int pending) if (bp == NULL) break; - if (nvd_bio_submit(ndisk, bp) != 0) { - continue; + if (__predict_false(bp->bio_flags & BIO_ORDERED)) { + /* + * bio with BIO_ORDERED flag set must be executed + * after all previous bios. + */ + while (ndisk->cur_depth > 0) + tsleep(&ndisk->cur_depth, 0, "nvdorb", 1); + } else { + /* + * bio with BIO_ORDERED flag set must be completed + * before proceeding with additional bios. + */ + while (ndisk->cur_depth >= NVD_ODEPTH) + tsleep(&ndisk->cur_depth, 0, "nvdora", 1); } -#ifdef BIO_ORDERED - /* - * BIO_ORDERED flag dictates that the bio with BIO_ORDERED - * flag set must be completed before proceeding with - * additional bios. - */ - if (bp->bio_flags & BIO_ORDERED) { - while (ndisk->cur_depth > 0) { - pause("nvd flush", 1); - } - } -#endif + nvd_bio_submit(ndisk, bp); } }
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